Onan carb fun

[benski]

:frown:
The 18 hp twin cylinder Onan on my 1978 Sears GT has got me baffled.
I changed out the fuel line,fuel filter, cleaned out the fuel pump, replaced the vacuum pump line for the fuel pump, checked the float level, cleaned all the passages inside the carb, sprayed carb cleaner through all the passages and now I've got the following problem;
The fuel comes up the vent in the top of the carb, then gets sucked into the carb throat, and of course it runs very rich and very poorly. Is there something I'm missing that's easy here?
After the thing sits for about 3 minutes, I can start it and it runs perfectly, until the fuel pumps up and fills the vent again, which takes about 15 seconds.

 

[reddragon]

i just rebuilt the carb on my 18/6......does it flood up the vent without running?

 

[benski]

i just rebuilt the carb on my 18/6......does it flood up the vent without running?

No. It takes about 10 to 15 seconds for the pump to fill up the vent after it is restarted.

 

[reddragon]

did this run before this happened?......its obviously flooding...so id check the needle/seat.....the vent on mine was in the throat near the choke plate...is that where yours is?....i had a plugged vent on a carb and it poured out thru the main jet because atmospheric pressure couldnt regulate...maybe its not the vent...but a bleed passage?

 

[KennyV]

Along with checking the float level... check for gasoline inside the float... if it has fuel in it it will sink and flood...
:smile:KennyV

 

[benski]

Mystery resolved!:biggrin: Today I went back to it, and rechecked everything I'd done, or thought I'd done. I took the top of the carb off, sprayed some carb cleaner into all the little passageways and jets, and then ran the smallest tip cleaner I have into all the holes, sprayed again with carb cleaner, and reassembled the thing, and fired it up.No gas coming out the vent, instantly running better, and with a little fine tuning a nice idle and a good, strong WOT. So, I wish I knew exactly what I did to rectify the situation, but I don't.:confused2: Must have been some small blockage preventing air from going where it needed to go,causing the carb to fill up completely with fuel. Heck, I'll take it!:smile:

 

[reddragon]

good to hear!.....sometimes that little speck of something likes to jump in there right as your reassembling a carb:confused2:

 

[benski]

good to hear!.....sometimes that little speck of something likes to jump in there right as your reassembling a carb:confused2:

Who would have thought a speck of something that small would be a cause of a 600 lb. machine not working smoothly?:wink::biggrin:Thanks to everyone for their ideas and responses.:thumbsup: